Method for fabricating optical devices by assembling multiple wafers containing planar optical waveguides

Abstract

A method for fabricating optical devices comprises the steps of preparing a first substrate wafer with at least one buried optical waveguide on an approximately flat planar surface of the substrate and a second substrate wafer with at least a second buried optical waveguide. The waveguides so formed may be straight or be curved along the surface of the wafer or curved by burying the waveguide at varying depth along its length. The second wafer is turned (flipped) and bonded to the first wafer in such a manner that the waveguides, for example, may form an optical coupler or may crossover one another and be in proximate relationship along a region of each. As a result, three dimensional optical devices are formed avoiding conventional techniques of layering on a single substrate wafer. Optical crossover angles may be reduced, for example, to thirty degrees from ninety degrees saving substrate real estate. Recessed areas may be provided in one or the other substrate surface reducing crosstalk in a completed three dimensional crossover device. Three dimensional optical couplers may comprise waveguides of identical or dissimilar characteristics. Moreover, three dimensional optical switches may be formed using the proposed flip and bond assembly process.

1. A method for fabricating a planar optical waveguide (POW) device comprising:
 forming a first optical waveguide in a first POW substrate, the first optical waveguide having a length extending approximately parallel to the first surface of the first POW substrate, with a first segment of the length of the first optical waveguide at a first depth beneath the first surface of the first POW substrate, and a second segment of the first optical waveguide at a second death beneath the first surface of the first POW substrate, where the first depth and the second depth are substantially different; 
 forming a second optical waveguide in a second POW substrate, the second optical waveguide having a length extending approximately parallel to the first surface of the second POW substrate, and 
 bonding the first surface of the first POW substrate to the first surface of the second POW substrate. 
 
   
   
     2. The method of  claim 1  wherein the first optical waveguide is formed with a first pattern and the second optical waveguide is formed with a second pattern and the first pattern does not match the second pattern. 
   
   
     3. The method of  claim 1 , in which the two POW substrates are composed of different materials. 
   
   
     4. The method of  claim 3 , in which at least one of the POW substrates is crystalline and another one of the POW substrates is non-crystalline. 
   
   
     5. The method of  claim 3 , in which the POW substrates contain waveguides with different refractive index profile from each other. 
   
   
     6. The method of  claim 1 , in which at least one POW substrate contains at least one active waveguide capable of providing optical gain. 
   
   
     7. The method of  claim 6 , in which the active waveguide comprises a semiconductor. 
   
   
     8. The method of  claim 6 , in which the active waveguide comprises rare earth ions. 
   
   
     9. The method of  claim 8 , in which the rare earth is erbium. 
   
   
     10. The method of  claim 1 , in which at least one of the optical waveguides provides saturable optical absorption. 
   
   
     11. The method of  claim 10 , in which the optical waveguide providing saturable optical absorption comprises a semiconductor. 
   
   
     12. The method of  claim 11 , in which the optical waveguide providing saturable optical absorption comprises rare earth ions. 
   
   
     13. The method of  claim 12 , in which the rare earth is erbium. 
   
   
     14. The method of  claim 1 , in which at least a segment of said first optical waveguide is positioned with respect to the second optical waveguide so that their guided waves interact to form an optical coupler. 
   
   
     15. The method of  claim 1 , in which at least a segment of said first optical waveguide is positioned with respect to the second optical waveguide so that their guided waves cross each other without strong interaction forming an optical crossover. 
   
   
     16. The method of  claim 1 , in which:
 at least a segment of said first optical waveguide is positioned with respect to the second optical waveguide so that their guided waves interact to form an optical coupler; and 
 at least a segment of said first optical waveguide is positioned with respect to the second optical waveguide so that their guided waves cross each other without strong interaction to form an optical crossover; and 
 the optical coupler and the optical crossover are interconnected to form an optical integrated circuit. 
 
   
   
     17. The method of  claim 1 , wherein the distance between the first waveguide and the first surface is varied along the length of the first waveguide so that the waveguide is curved with respect to the first surface of the first POW substrate to produce a curved waveguide. 
   
   
     18. The method of  claim 1 , in which a region of low refractive index is formed between the first and second optical waveguides to control the degree of coupling between them. 
   
   
     19. The method of  claim 1 , in which a region of high refractive index is formed between the first and second optical waveguides to control the degree of coupling between them. 
   
   
     20. The method of  claim 1  forming a second optical waveguide in a second POW substrate, the second optical waveguide having a length extending in a first direction approximately parallel to the first surface of the second POW substrate, with a first segment of the length of the second optical waveguide at a first depth beneath the first surface of the second POW substrate, and a second segment of the second optical waveguide at a second depth beneath the first surface of the second POW substrate, where the first depth and the second depth are substantially different.